Local control of multiple context processing elements with configuration contexts

ABSTRACT

A method and apparatus for providing local control of processing elements in a network of multiple context processing elements (MCPEs). A MCPE stores configuration memory contexts and maintains data of a current configuration. State information is received from at least one other MCPE. A configuration control signal is generated in response to the state information and current configuration data. A MCPE is selected in response to the configuration control signal to control the MCPE. Each MCPE in the networked array has an assigned physical and virtual identification. Data comprising control data, configuration data, an address mask, and a destination identification is transmitted to a MCPE. The transmitted address mask is applied to either a physical or a virtual identification, and to a destination identification. The masked physical or virtual identification is compared to the masked destination identification. When the masked physical or virtual identification matches the masked destination identification, a MCPE is manipulated in response to the transmitted data by selecting one of a number of configuration memory contexts to control the functioning of the MCPE.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of application Ser. No.10/210,411, filed on Jul. 31, 2002, now issued U.S. Pat. No. 6,553,479which is a continuation of application Ser. No. 09/322,291, filed on May28, 1999, U.S. Pat. No. 6,457,116, which is a continuation ofapplication Ser. No. 08/962,141, filed Oct. 31, 1997, U.S. Pat. No.5,915,123, priority of each of which are hereby claimed.

FIELD OF THE INVENTION

This invention relates to array based computing devices. Moreparticularly, this invention relates to a semiconductor chiparchitecture that provides for local control of field programmable gatearrays in a network configuration.

BACKGROUND OF THE INVENTION

Advances in semiconductor technology have greatly increased theprocessing power of a single chip general purpose computing device. Therelatively slow increase in the inter-chip communication bandwidthrequires modern high performance devices to use as much of the potentialon chip processing power as possible. This results in large, denseintegrated circuit devices and a large design space of processingarchitectures. This design space is generally viewed in terms ofgranularity, wherein granularity dictates that designers have the optionof building very large processing units, or many smaller ones, in thesame silicon area. Traditional architectures are either very coarsegrain, like microprocessors, or very fine grain, like field programmablegate arrays (FPGAs).

Microprocessors, as coarse grain architecture devices, incorporate a fewlarge processing units that operate on wide data words, each unit beinghardwired to perform a defined set of instructions on these data words.Generally, each unit is optimized for a different set of instructions,such as integer and floating point, and the units are generallyhardwired to operate in parallel. The hardwired nature of these unitsallows for very rapid instruction execution. In fact, a great deal ofarea on modern microprocessor chips is dedicated to cache memories inorder to support a very high rate of instruction issue. Thus, thedevices efficiently handle very dynamic instruction streams.

Most of the silicon area of modern microprocessors is dedicated tostoring data and instructions and to control circuitry. Therefore, mostof the silicon area is dedicated to allowing computational tasks toheavily reuse the small active portion of the silicon, the arithmeticlogic units (ALUs). Consequently very little of the capacity inherent ina processor gets applied to the problem; most of the capacity goes intosupporting a high diversity of operations.

Field programmable gate arrays, as very fine grain devices, incorporatea large number of very small processing elements. These elements arearranged in a configurable interconnected network. The configurationdata used to define the functionality of the processing units and thenetwork can be thought of as a very large semantically powerfulinstruction word allowing nearly any operation to be described andmapped to hardware.

Conventional FPGAs allow finer granularity control over processoroperations, and dedicate a minimal area to instruction distribution.Consequently, they can deliver more computations per unit of siliconthan processors, on a wide range of operations. However, the lack ofresources for instruction distribution in a network of prior artconventional FPGAs make them efficient only when the functionaldiversity is low, that is when the same operation is required repeatedlyand that entire operation can be fit spatially onto the FPGAs in thesystem.

Furthermore, in prior art FPGA networks, retiming of data is oftenrequired in order to delay data. This delay is required because datathat is produced by one processing element during one clock cycle maynot be required by another processing element until several clock cyclesafter the clock cycle in which it was made available. One prior arttechnique for dealing with this problem is to configure some processingelements to function as memory devices to store this data. Another priorart technique configures processing elements as delay registers to beused in the FPGA network. The problem with both of these prior arttechnique is that valuable silicon is wasted by using processingelements as memory and delay registers.

Dynamically programmable gate arrays (DPGAs) dedicate a modest amount ofon-chip area to store additional instructions allowing them to supporthigher operational diversity than traditional FPGAs. However, thesilicon area necessary to support this diversity must be dedicated atfabrication time and consumes area whether or not the additionaldiversity is required. The amount of diversity supported, that is, thenumber of instructions supported, is also fixed at fabrication time.Furthermore, when regular data path operations are required allinstruction stores are required to be programmed with the same datausing a global signal broadcasted to all DPGAs.

The limitations present in the prior art FPGA and DPGA networks in theform of limited control over configuration of the individual FPGAs andDPGAs of the network severely limits the functional diversity of thenetworks. For example, in one prior art FPGA network, all FPGAs must beconfigured at the same time to contain the same configurations.Consequently, rather than separate the resources for instruction storageand distribution from the resources for data storage and computation,and dedicate silicon resources to each of these resources at fabricationtime, there is a need for an architecture that unifies these resources.Once unified, traditional instruction and control resources can bedecomposed along with computing resources and can be deployed in anapplication specific manner. Chip capacity can be selectively deployedto dynamically support active computation or control reuse ofcomputational resources depending on the needs of the application andthe available hardware resources.

SUMMARY OF THE INVENTION

A method and apparatus for providing local control of processingelements in a network of multiple context processing element areprovided. According to one aspect of the invention, a multiple contextprocessing element is configured to store a number of configurationmemory contexts. This multiple context processing element maintains dataof a current configuration. State information is received from at leastone other multiple context processing element. The state informationcomprises at least one bit received over a multiple level network, thebit representative of at least one configuration memory context of themultiple context processing element from which it is received. At leastone configuration control signal is generated in response to the stateinformation and the data of a current configuration. One of multipleconfiguration memory contexts is selected in response to the receivedstate information and the data of a current configuration. The selectedconfiguration memory context controls the multiple context processingelement.

Each multiple context processing element in the networked array ofmultiple context processing elements has an assigned physical andvirtual identification. Data is transmitted to at least one of themultiple context processing elements of the array, the data comprisingcontrol data, configuration data, an address mask, and a destinationidentification. The transmitted address mask is applied to either thephysical or virtual identification and to a destination identification.The masked physical or virtual identification is compared to the maskeddestination identification. When the masked physical or virtualidentification of a multiple context processing element matches themasked destination identification, at least one of the number ofmultiple context processing elements are manipulated in response to thetransmitted data. Manipulation comprises selecting one of a number ofconfiguration memory contexts to control the functioning of the multiplecontext processing element.

These and other features, aspects, and advantages of the presentinvention will be apparent from the accompanying drawings and from thedetailed description and appended claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 is the overall chip architecture of one embodiment. This chiparchitecture comprises many highly integrated components.

FIG. 2 is an eight bit MCPE core of one embodiment of the presentinvention.

FIG. 3 is a data flow diagram of the MCPE of one embodiment.

FIG. 4 is the level 1 network of one embodiment.

FIG. 5 is the level 2 network of one embodiment.

FIG. 6 is the level 3 network of one embodiment.

FIG. 7 is the broadcast, or configuration, network used in oneembodiment.

FIG. 8 is the encoding of the configuration byte stream as received bythe CNI in one embodiment.

FIG. 9 is the encoding of the command/context byte in one embodiment.

FIG. 10 is a flowchart of a broadcast network transaction.

FIG. 11 is the MCPE networked array with delay circuits of oneembodiment.

FIG. 12 is a delay circuit of one embodiment.

FIG. 13 is a delay circuit of an alternate embodiment.

FIG. 14 is a processing element (PE) architecture which is a simplifiedversion of the MCPE architecture of one embodiment.

FIG. 15 is the MCPE configuration memory structure of one embodiment.

FIG. 16 shows the major components of the MCPE control logic structureof one embodiment.

FIG. 17 is the FSM of the MCPE configuration controller of oneembodiment.

FIG. 18 is a flowchart for manipulating a networked array of MCPEs inone embodiment.

FIG. 19 shows the selection of MCPEs using an address mask in oneembodiment.

FIG. 20 illustrates an 8-bit processor configuration of a reconfigurableprocessing device which has been constructed and programmed according toone embodiment.

FIG. 21 illustrates a single instruction multiple data systemconfiguration of a reconfigurable processing device of one embodiment.

FIG. 22 illustrates a 32-bit processor configuration of a reconfigurableprocessing device which has been constructed and programmed according toone embodiment.

FIG. 23 illustrates a multiple instruction multiple data systemconfiguration of a reconfigurable processing device of one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A method and an apparatus for retiming in a network of multiple contextprocessing elements are provided. In the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be evident, however, to one skilled in the art that the presentinvention may be practiced without these specific details. In otherinstances, well-known structures and devices are shown in block diagramform in order to avoid unnecessarily obscuring the present invention.

FIG. 1 is the overall chip architecture of one embodiment. This chiparchitecture comprises many highly integrated components. While priorart chip architectures fix resources at fabrication time, specificallyinstruction source and distribution, the chip architecture of thepresent invention is flexible. This architecture uses flexibleinstruction distribution that allows position independent configurationand control of a number of multiple context processing elements (MCPEs)resulting in superior performance provided by the MCPEs. The flexiblearchitecture of the present invention uses local and global control toprovide selective configuration and control of each MCPE in an array;the selective configuration and control occurs concurrently with presentfunction execution in the MCPEs.

The chip of one embodiment of the present invention is composed of, butnot limited to, a 10×10 array of identical eight-bit functional units,or MCPEs 102, which are connected through a reconfigurable interconnectnetwork. The MCPEs 102 serve as building blocks out of which a widevariety of computing structures may be created. The array size may varybetween 2×2 MCPEs and 16×16 MCPEs, or even more depending upon theallowable die area and the desired performance. A perimeter networkring, or a ring of network wires and switches that surrounds the corearray, provides the interconnect between the MCPEs and perimeterfunctional blocks.

Surrounding the array are several specialized units that may performfunctions that are too difficult or expensive to decompose into thearray. These specialized units may be coupled to the array usingselected MCPEs from the array. These specialized units can include largememory blocks called configurable memory blocks 104. In one embodimentthese configurable memory blocks 104 comprise eight blocks, two perside, of 4 kilobyte memory blocks. Other specialized units include atleast one configurable instruction decoder 106.

Furthermore, the perimeter area holds the various interfaces that thechip of one embodiment uses to communicate with the outside worldincluding: input/output (I/O) ports; a peripheral component interface(PCI) controller, which may be a standard 32-bit PCI interface; one ormore synchronous burst static random access memory (SRAM) controllers; aprogramming controller that is the boot-up and master control block forthe configuration network; a master clock input and phase-locked loop(PLL) control/configuration; a Joint Test Action Group (JTAG) testaccess port connected to all the serial scan chains on the chip; and I/Opins that are the actual pins that connect to the outside world.

FIG. 2 is an eight bit MCPE core of one embodiment of the presentinvention. Primarily the MCPE core comprises memory block 210 and basicALU core 220. The main memory block 210 is a 256 word by eight bit widememory, which is arranged to be used in either single or dual portmodes. In dual port mode the memory size is reduced to 128 words inorder to be able to perform two simultaneous read operations withoutincreasing the read latency of the memory. Network port A 222, networkport B 224, ALU function port 232, control logic 214 and 234, and memoryfunction port 212 each have configuration memories (not shown)associated with them. The configuration memories of these elements aredistributed and are coupled to a Configuration Network Interface (CNI)(not shown) in one embodiment. These connections may be serialconnections but are not so limited. The CNI couples all configurationmemories associated with network port A 222, network port B 224, ALUfunction port 232, control logic 214 and 234, and memory function port212 thereby controlling these configuration memories. The distributedconfiguration memory stores configuration words that control theconfiguration of the interconnections. The configuration memory alsostores configuration information for the control architecture.Optionally it can also be a multiple context memory that receivescontext selecting signals broadcasted globally and locally from avariety of sources.

The structure of each MCPE allows for a great deal of flexibility whenusing the MCPEs to create networked processing structures. FIG. 3 is adata flow diagram of the MCPE of one embodiment. The major components ofthe MCPE include static random access memory (SRAM) main memory 302, ALUwith multiplier and accumulate unit 304, network ports 306, and controllogic 308. The solid lines mark data flow paths while the dashed linesmark control paths; all of the lines are one or more bits wide in oneembodiment. There is a great deal of flexibility available within theMCPE because most of the major components may serve several differentfunctions depending on the MCPE configuration.

The MCPE main memory 302 is a group of 256 eight bit SRAM cells that canoperate in one of four modes. It takes in up to two eight bit addressesfrom A and B address/data ports, depending upon the mode of operation.It also takes in up to four bytes of data, which can be from fourfloating ports, the B address/data port, the ALU output, or the highbyte from the multiplier. The main memory 302 outputs up to four bytesof data. Two of these bytes, memory A and B, are available to the MCPE'sALU and can be directly driven onto the level 2 network. The other twobytes, memory C and D, are only available to the network. The output ofthe memory function port 306 controls the cycle-by-cycle operation ofthe memory 302 and the internal MCPE data paths as well as the operationof some parts of the ALU 304 and the control logic 308. The MCPE mainmemory may also be implemented as a static register file in order tosave power.

Each MCPE contains a computational unit 304 comprised of threesemi-independent functional blocks. The three semi-independentfunctional blocks comprise an eight bit wide ALU, an 8×8 to sixteen bitmultiplier, and a sixteen bit accumulator. The ALU block, in oneembodiment, performs logical, shift, arithmetic, and multiplicationoperations, but is not so limited. The ALU function port 306 specifiesthe cycle-by-cycle operation of the computational unit. Thecomputational units in orthogonally adjacent MCPEs can be chained toform wider-word datapaths.

The MCPE network ports connect the MCPE network to the internal MCPElogic (memory, ALU, and control). There are eight ports in each MCPE,each serving a different set of purposes. The eight ports comprise twoaddress/data ports, two function ports, and four floating ports. The twoaddress/data ports feed addresses and data into the MCPE memories andALU. The two function ports feed instructions into the MCPE logic. Thefour floating ports may serve multiple functions. The determination ofwhat function they are serving is made by the configuration of thereceivers of their data.

The MCPEs of one embodiment are the building blocks out of which morecomplex processing structures may be created. The structure that joinsthe MCPE cores into a complete array in one embodiment is actually a setof several mesh-like interconnect structures. Each interconnectstructure forms a network, and each network is independent in that ituses different paths, but the networks do join at the MCPE inputswitches. The network structure of one embodiment of the presentinvention is comprised of a local area broadcast network (level 1), aswitched interconnect network (level 2), a shared bus network (level 3),and a broadcast, or configuration, network.

FIG. 4 is the level 1 network of one embodiment. The level 1 network, orbit-wide local interconnect, consists of direct point-to-pointcommunications between each MCPE 702 and the eight nearest neighbors704. Each MCPE 702 can output up to 12 values comprising two in each ofthe orthogonal directions, and one in each diagonal. The level 1 networkcarries bit-oriented control signals between these local groups ofMCPEs. The connections of level 1 only travel one MCPE away, but thevalues can be routed through the level 1 switched mesh structure toother MCPEs 706. Each connection consists of a separate input and outputwire. Configuration for this network is stored along with MCPEconfiguration.

FIG. 5 is the level 2 network of one embodiment. The level 2 network, orbyte-wide local interconnect, is used to carry data, instructions, oraddresses in local groups of MCPEs 650. It is a byte-wide version oflevel 1 having additional connections. This level uses relatively shortwires linked through a set of switches. The level 2 network is theprimary means of local and semi-local MCPE communication, and level 2does require routing. Using the level 2 network each MCPE 650 can outputup to 16 values, at least two in each of the orthogonal directions andat least one in each diagonal. Each connection consists of separateinput and output wires. These connections only travel one MCPE away, butthe values can be routed through level 2 switches to other MCPEs.Preferable configuration for this network is also stored along with MCPEconfiguration.

FIG. 6 is the level 3 network of one embodiment. In this one embodiment,the level 3 network comprises connections 852 of four channels betweeneach pair of MCPEs 854 and 856 arranged along the major axes of the MCPEarray providing for communication of data, instructions, and addressesbetween groups of MCPEs and between MCPEs and the perimeter of the chip.Preferable communication using the level 3 network is bi-directional anddynamically routable. A connection between two endpoints through aseries of level 3 array and periphery nodes is called a “circuit” andmay be set up and taken down by the configuration network. In oneembodiment, each connection 852 consists of an 8-bit bi-directionalport.

FIG. 7 is the broadcast, or configuration, network used in oneembodiment. This broadcast network is an H-tree network structure with asingle source and multiple receivers in which individual MCPEs 1002 maybe written to. This broadcast network is the mechanism by whichconfiguration memories of both the MCPEs and the perimeter units getprogrammed. The broadcast network may also be used to communicate theconfiguration data for the level 3 network drivers and switches.

The broadcast network in one embodiment comprises a nine bit broadcastchannel that is structured to both program and control the on-chip MCPE1002 configuration memories. The broadcast network comprises a centralsource, or Configuration Network Source (CNS) 1004, and oneConfiguration Network Interface (CNI) block 1006 for each majorcomponent, or one in each MCPE with others assigned to individual orgroups of non-MCPE blocks. The CNI 1006 comprises a hardwired finitestate machine, several state registers, and an eight bit loadableclearable counter used to maintain timing. The CNS 1004 broadcasts tothe CNIs 1006 on the chip according to a specific protocol. The networkis arranged so that the CNIs 1006 of one embodiment receive thebroadcast within the same clock cycle. This allows the broadcast networkto be used as a global synchronization mechanism as it has a fixedlatency to all parts of the chip. Therefore, the broadcast networkfunctions primarily to program the level 3 network, and to preparereceiving CNIs for configuration transactions. Typically, the bulk ofconfiguration data is carried over the level 3 network, however thebroadcast network can also serve that function. The broadcast networkhas overriding authority over any other programmable action on the chip.

A CNI block is the receiving end of the broadcast network. Each CNI hastwo addresses: a physical, hardwired address and a virtual, programmableaddress. The latter can be used with a broadcast mask, discussed herein,that allows multiple CNIs to receive the same control and programmingsignals. A single CNI is associated with each MCPE in the networked MCPEarray. This CNI controls the reading and writing of the configuration ofthe MCPE contexts, the MCPE main memory, and the MPCE configurationcontroller.

The CNS 1004 broadcasts a data stream to the CNIs 1006 that comprisesthe data necessary to configure the MCPEs 1002. In one embodiment, thisdata comprises configuration data, address mask data, and destinationidentification data. FIG. 8 is the encoding of the configuration bytestream as received by the CNI in one embodiment. The first four bytesare a combination of mask and address where both mask and address are 15bit values. The address bits are only tested when the corresponding maskis set to “1”. The high bit of the Address High Byte is aVirtual/Physical identification selection. When set to “1”, the maskedaddress is compared to the MCPE virtual, or programmable,identification; when set to “0” the masked address is compared to theMCPE physical address. This address scheme applies to a CNI blockwhether or not it is in an MCPE.

Following the masked address is a command/context byte which specifieswhich memory will be read from or written to by the byte stream. FIG. 9is the encoding of the command/context byte in one embodiment. Followingthe command/context byte is a byte-count value. The byte count indicatesthe number of bytes that will follow.

As previously discussed, the CNS 1004 broadcasts a data stream to theCNIs 1006 that comprises the data necessary to configure the MCPEs 1002.In one embodiment, this data comprises configuration data, address maskdata, and destination identification data. A configuration networkprotocol defines the transactions on the broadcast network. FIG. 10 is aflowchart 800 of one embodiment of a broadcast network transaction. Inthis embodiment, a transaction can contain four phases: global address802, byte count 804, command 806, and operation 808. The command 806 andoperation 808 phases may be repeated as much as desired within a singletransaction.

The global address phase 802 is used to select a particular receiver orreceivers, or CNI blocks, and all transactions of an embodiment beginwith the global address phase 802. This phase 802 comprises two modes, aphysical address mode and a virtual address mode, selected, for example,using a prespecified bit of a prespecified byte of the transaction. Thephysical address mode allows the broadcast network to select individualCNIs based on hardwired unique identifiers. The virtual address mode isused to address a single or multiple CNIs by a programmable identifierthereby allowing the software to design its own address space. At theend of the global address phase 802, the CNIs know whether they havebeen selected or not.

Following the global address phase 802, a byte count 804 of thetransaction is transmitted so as to allow both selected and unselectedCNIs to determine when the transaction ends. The selected CNIs enter thecommand phase 806; the CNIs not selected watch the transaction 818 andwait 816 for the duration of the byte count. It is contemplated thatother processes for determining the end of a transaction may also beused.

During the command phase 806, the selected CNIs can be instructed towrite the data on the next phase into a particular context,configuration, or main memory (write configuration data 814), to listento the addresses, commands and data coming over the network (networkmastered transaction 812), or to dump the memory data on to a networkoutput (dump memory data 810). Following the command phase 806, the datais transmitted during the operation phase 808.

The network mastered transaction mode 812 included in the presentembodiment commands the CNI to look at the data on the output of thelevel 3 network. This mode allows multiple configuration processes totake place in parallel. For example, a level 3 connection can beestablished between an off chip memory, or configuration storage, and agroup of MCPEs and the MCPEs all commanded to enter the network masteredmode. This allows those MCPEs to be configured, while the broadcastnetwork can be used to configure other MCPEs or establish additionallevel 3 connections to other MCPEs.

Following completion of the operation phase 808, the transaction mayissue a new command, or it can end. If it ends, it can immediately befollowed by a new transaction. If the byte count of the transaction hasbeen completed, the transaction ends. Otherwise, the next byte isassumed to be a new command byte.

Pipeline delays can be programmed into the network structure as they areneeded. These delays are separate from the networked array of MCPEs andprovide data-dependent retiming under the control of the configurationmemory context of a MCPE, but do not require an MCPE to implement thedelay. In this way, processing elements are not wasted in order toprovide timing delays. FIG. 11 is the MCPE networked array 2202 withdelay circuits 2204-2208 of one embodiment. The subsets of the outputsof the MCPE array 2202 are coupled to the inputs of a number of delaycircuits 2204-2208. In this configuration, a subset comprising sevenMCPE outputs share each delay circuit, but the configuration is not solimited. The outputs of the delay circuits 2204-2208 are coupled to amultiplexer 2210 that multiplexes the delay circuit outputs to a systemoutput 2212. In this manner, the pipeline delays can be selectivelyprogrammed for the output of each MCPE of the network of MCPEs. Theconfiguration memory structure and local control described herein areshared between the MCPEs and the delay circuit structure.

FIG. 12 is a delay circuit 2400 of one embodiment. This circuitcomprises three delay latches 2421-2423, a decoder 2450, and twomultiplexers 2401-2402, but is not so limited. Some number N of MCPEoutputs of a network of MCPEs are multiplexed into the delay circuit2400 using a first multiplexer 2401. The output of a MCPE selected bythe first multiplexer 2401 is coupled to a second multiplexer 2402 andto the input of a first delay latch 2421. The output of the first delaylatch 2421 is coupled to the input of a second delay latch 2422. Theoutput of the second delay latch 2422 is coupled to the input of a thirddelay latch 2423. The output of the third delay latch 2423 is coupled toan input of the second multiplexer 2402. The output of the secondmultiplexer 2402 is the delay circuit output. A decoder 2450 selectivelyactivates the delay latches 2421-2423 via lines 2431-2433, respectively,thereby providing the desired amount of delay. The decoder is coupled toreceive via line 2452 at least one set of data representative of atleast one configuration memory context of a MCPE and control latches2421-2423 in response thereto. The MCPE having it's output coupled tothe delay circuit 2400 by the first multiplexer 2402 may be the MCPEthat is currently selectively coupled to the decoder 2450 via line 2452,but is not so limited. In an alternate embodiment, the MCPE receivingthe output 2454 of the delay circuit 2400 from the second multiplexer2402 may be the MCPE that is currently selectively coupled to thedecoder 2450 via line 2452, but is not so limited.

FIG. 13 is a delay circuit 2100 of an alternate embodiment. This circuitcomprises three delay registers 2121-2123 and three multiplexers2101-2103, but is not so limited. Several outputs of a network of MCPEsare multiplexed into the delay circuit 2100 using a first multiplexer2101. The output of a MCPE selected by the first multiplexer 2101 iscoupled to a second multiplexer 2102 and the input of a first delayregister 2121. The output of the first delay register 2121 is coupled toan input of a third multiplexer 2103 and the input of a second delayregister 2122. The output of the second delay register 2122 is coupledto an input of the third multiplexer 2103 and the input of a third delayregister 2123. The output of the third delay register 2123 is coupled toan input of the third multiplexer 2103. The output of the thirdmultiplexer 2103 is coupled to an input of the second multiplexer 2102,and the output of the second multiplexer 2102 is the delay circuitoutput.

Each of the second and third multiplexers 2102 and 2103 are coupled toreceive via lines 2132 and 2134, respectively, at least one set of datarepresentative of at least one configuration memory context of a MCPE.Consequently, the MCPE coupled to control the second and thirdmultiplexers 2102 and 2104 may be the MCPE that is currently selectivelycoupled to the delay circuit 2100 by multiplexer 2101, but is not solimited. The control bits provided to multiplexer 2102 cause multiplexer2102 to select the undelayed output of multiplexer 2101 or the delayedoutput of multiplexer 2103. The control bits provided to multiplexer2103 cause multiplexer 2103 to select a signal having a delay of aparticular duration. When multiplexer 2103 is caused to select line 2141then the delay duration is that provided by one delay register, delayregister 2121. When multiplexer 2103 is caused to select line 2142 thenthe delay duration is that provided by two delay registers, delayregisters 2121 and 2122. When multiplexer 2103 is caused to select line2143 then the delay duration is that provided by three delay registers,delay registers 2121, 2122, and 2123.

The control logic of the MCPE of one embodiment is designed to allowdata dependent changes in the MCPE operation. It does so by changing theMCPE configuration contexts which in turn change the MCPE functionality.In order to describe the use of configuration contexts, an architectureis described to which they apply. FIG. 14 is a processing element (PE)architecture which is a simplified version of the MCPE architecture ofone embodiment. In this PE architecture, each PE has three input ports:the ALU port; the Data port; and the External control port. The controlstore 1202 is sending the processing unit 1204 microcode instructions1210 and the program counter 1206 jump targets 1212. The control store1202 takes the address of its next microcode instruction 1214 from theprogram counter 1206. The processing unit 1204 is taking theinstructions 1210 from the control store 1202, as well as data notshown, and is performing the microcoded operations on that data. One ofthe results of this operation is the production of a control signal 1216that is sent to the program counter 1206. The program counter 1206performs one of two operations, depending on the value of the controlsignal from the processing unit 1204. It either adds one to the presentvalue of the program counter 1206, or it loads the program counter 1206with the value provided by the control store 1202.

The ports in each PE can either be set to a constant value or be set toreceive their values from another PE. When the port is set to load thevalue from another PE it is said to be in a static mode. Each PE has aregister file and the value presented at the ALU control port caninstruct the PE to increment an element in its register file or load anelement in its register file from the data port. The state of each portthen is comprised by its port mode, which is constant or static. If theport mode is constant then its state also includes the constant value.

The PEs have multiple contexts. These contexts define the port state foreach port. The PEs also have a finite state machine (FSM) that isdescribed as a two index table that takes the current context as thefirst index and the control port as the second index. For this example,assume that there are two contexts, 0 and 1, and there are two values tothe control signal 0 and 1.

Now considered is the creation of the program counter 1206 from the PEs.The definition of the context 0 for the program counter 1206 is that theALU control port is set to a constant value such that the PE willincrement its first register. The state of the data port is static andset to input the branch target output from the control store 1202. Thestate of the control port is static and set to input the control outputfrom the processing unit 1204. The definition of context 1 is that theALU control port is set to a constant value such that the PE will loadits first register with the value of the data port. The state of thedata port is static and set to input the branch target output from thecontrol store 1202. The state of the control port is static and set toinput the control output from the processing unit 1204. In all contextsthe unit is sending the value of its first register to the control storeas its next address.

Now considered is the operation of this PE unit. The PE is placed intocontext 0 upon receiving a 0 control signal from the processing unit1204. In this context it increments its first register so that theaddress of the next microcode instruction is the address following theone of the present instruction. When the PE receives a 1 control signalfrom the processing unit it is placed in context 1. In this context itloads its first register with the value received on the data port. ThisPE is therefore using the context and the FSM to vary its function atrun time and thereby perform a relatively complex function.

FIG. 15 is the MCPE configuration memory structure of one embodiment.Each MCPE has four major contexts 402-408 of configuration memory. Eachcontext contains a complete set of data to fully describe the operationof the MCPE, including the local network switching. In one embodimenttwo of the contexts are hardwired and two are programmable. Each ofthese contexts includes two independently writable minor contexts. Inthe programmable major contexts the minor contexts are a duplication ofpart of the MCPE configuration consisting primarily of the portconfigurations. In the hardwired major contexts the minor contexts maychange more than just the port configurations. The switching of theseminor contexts is also controlled by the configuration control. Theminor contexts are identical in structure but contain different run-timeconfigurations. This allows a greater degree of configurationflexibility because it is possible to dynamically swap some parts of theconfiguration without requiring memories to store extra major contexts.These minor contexts allow extra flexibility for important parts of theconfiguration while saving the extra memory available for those partsthat don't need to be as flexible. A configuration controller 410 finitestate machine (FSM) determines which context is active on each cycle.Furthermore, a global configuration network can force the FSM to changecontexts.

The first two major contexts (0 and 1) may be hardwired, or set duringthe design of the chip, although they are not so limited. Major context0 is a reset state that serves two primary roles depending on the minorcontext. Major context 1 is a local stall mode. When a MCPE is placedinto major context 1 it continues to use the configuration setting ofthe last non-context 1 cycle and all internal registers are frozen. Thismode allows running programs to stall as a freeze state in which nooperations occur but allows programming and scan chain readout, fordebugging, to occur.

Minor context 0 is a clear mode. Minor context 0 resets all MCPEregisters to zero, and serves as the primary reset mode of the chip.Minor context 0 also freezes the MCPE but leaves the main memory activeto be read and written over by the configuration network.

Minor context 1 is a freeze mode. In this mode the internal MCPEregisters are frozen while holding their last stored value; thisincludes the finite state machine state register. This mode can be usedas a way to turn off MCPE's that are not in use or as a reset state.Minor context 1 is useful to avoid unnecessary power consumption inunused MCPEs because the memory enable is turned off during this mode.

Major contexts 2 and 3 are programmable contexts for user definedoperations. In addition to the four major contexts the MCPE containssome configurations that do not switch under the control of theconfiguration controller. These include the MCPE's identification numberand the configuration for the controller itself.

FIG. 16 shows the major components of the MCPE control logic structureof one embodiment. The Control Tester 602 takes the output of the ALUfor two bytes from floating ports 604 and 606, plus the left and rightcarryout bits, and performs a configurable test on them. The result isone bit indicating that the comparison matched. This bit is referred toas the control bit. This Control Tester serves two main purposes. Firstit acts as a programmable condition code generator testing the ALUoutput for any condition that the application needs to test for.Secondly, since these control bits can be grouped and sent out acrossthe level 2 and 3 networks, this unit can be used to perform a second orlater stage reduction on a set of control bits/data generated by otherMCPE's.

The level 1 network 608 carries the control bits. As previouslydiscussed, the level 1 network 608 consists of direct point-to-pointcommunications between every MCPE and it's 12 nearest neighbors. Thus,each MCPE will receive 13 control bits (12 neighbors and it's own) fromthe level 1 network. These 13 control bits are fed into the ControlReduce block 610 and the BFU input ports 612. The Control Reduce block610 allows the control information to rapidly effect neighboring MCPEs.The MCPE input ports allow the application to send the control dataacross the normal network wires so they can cover long distances. Inaddition the control bits can be fed into MCPEs so they can bemanipulated as normal data.

The Control Reduce block 610 performs a simple selection on either thecontrol words coming from the level 1 control network, the level 3network, or two of the floating ports. The selection control is part ofthe MCPE configuration. The Control Reduce block 610 selection resultsin the output of five bits. Two of the output bits are fed into the MCPEconfiguration controller 614. One output bit is made available to thelevel 1 network, and one output bit is made available to the level 3network.

The MCPE configuration controller 614 selects on a cycle-by-cycle basiswhich context, major or minor, will control the MCPE's activities. Thecontroller consists of a finite state machine (FSM) that is an activecontroller and not just a lookup table. The FSM allows a combination oflocal and global control over time that changes. This means that anapplication may run for a period based on the local control of the FSMwhile receiving global control signals that reconfigure the MCPE, or ablock of MCPEs, to perform different functions during the next clockcycle. The FSM provides for local configuration and control by locallymaintaining a current configuration context for control of the MCPE. TheFSM provides for global configuration and control by providing theability to multiplex and change between different configuration contextsof the MCPE on each different clock cycle in response to signalsbroadcasted over a network. This configuration and control of the MCPEis powerful because it allows an MCPE to maintain control during eachclock cycle based on a locally maintained configuration context whileproviding for concurrent global on-the-fly reconfiguration of each MCPE.This architecture significantly changes the area impact andcharacterization of an MCPE array while increasing the efficiency of thearray without wasting other MCPEs to perform the configuration andcontrol functions.

FIG. 17 is the FSM of the MCPE configuration controller of oneembodiment. In controlling the functioning of the MCPE, controlinformation 2004 is received by the FSM 2002 in the form of stateinformation from at least one surrounding MCPE in the networked array.This control information is in the form of two bits received from theControl Reduce block of the MCPE control logic structure. In oneembodiment, the FSM also has three state bits that directly control themajor and minor configuration contexts for the particular MCPE. The FSMmaintains the data of the current MCPE configuration by using a feedbackpath 2006 to feed back the current configuration state of the MCPE ofthe most recent clock cycle. The feedback path 2006 is not limited to asingle path. The FSM selects one of the available configuration memorycontexts for use by the corresponding MCPE during the next clock cyclein response to the received state information from the surrounding MCPEsand the current configuration data. This selection is output from theFSM in the form of a configuration control signal 2008. The selection ofa configuration memory context for use during the next clock cycleoccurs, in one embodiment, during the execution of the configurationmemory context selected for the current clock cycle.

FIG. 18 is a flowchart for manipulating a networked array of MCPEs inone embodiment. Each MCPE of the networked array is assigned a physicalidentification which, in one embodiment, is assigned at the time ofnetwork development. This physical identification may be based on theMCPE's physical location in the networked array. Operation begins atblock 1402, at which a virtual identification is assigned to each of theMCPEs of the array. The physical identification is used to address theMCPEs for reprogramming of the virtual identification because thephysical identification is accessible to the programmer. The assignedvirtual identification may be initialized to be the same as the physicalidentification. Data is transmitted to the MCPE array using thebroadcast, or configuration, network, at block 1404. The transmitteddata comprises an address mask, a destination identification, MCPEconfiguration data, and MCPE control data. The transmitted data also maybe used in selecting between the use of the physical identification andthe virtual identification in selecting MCPEs for manipulation.Furthermore, the transmitted data may be used to change the virtualidentification of the MCPEs. The transmitted data in one embodiment istransmitted from another MCPE. In an alternate embodiment, thetransmitted data is transmitted from an input/output device. In anotheralternate embodiment, the transmitted data is transmitted from an MCPEconfiguration controller. The transmitted data may also be transmittedfrom multiple sources at the same time.

The address mask is applied, at block 1408, to the virtualidentification of each MCPE and to the transmitted destinationidentification. The masked virtual identification of each MCPE iscompared to the masked destination identification, at block 1410, usinga comparison circuit. When a match is determined between the maskedvirtual identification of a MCPE and the masked destinationidentification, at block 1412, the MCPE is manipulated in response tothe transmitted data, at block 1414. The manipulation is performed usinga manipulation circuit. When no match is determined between the maskedvirtual identification of a MCPE, at block 1412, the MCPE is notmanipulated in response to transmitted data, at block 1416. In oneembodiment, a MCPE comprises the comparison circuit and the manipulationcircuit.

FIG. 19 shows the selection of MCPEs using an address mask in oneembodiment. The selection of MCPEs for configuration and control, aspreviously discussed, is determined by applying a transmitted mask toeither the physical address 1570 or the virtual address 1572 of theMCPEs 1550-1558. The masked address is then compared to a maskeddestination identification. For example, MCPEs 1550-1558 have physicaladdresses 0-8, respectively. MCPE 1550 has virtual address 0000. MCPE1551 has virtual address 0001. MCPE 1552 has virtual address 0010. MCPE1553 has virtual address 0100. MCPE 1554 has virtual address 0101. MCPE1555 has virtual address 0110. MCPE 1556 has virtual address 1000. MCPE1557 has virtual address 1100. MCPE 1558 has virtual address 1110. Inthis example, the virtual address 1572 will be used to select the MCPEs,so the mask will be applied to the virtual address 1572. The mask isused to identify the significant bits of the virtual address 1572 thatare to be compared against the significant bits of the maskeddestination identification in selecting the MCPEs. When mask (0011) istransmitted, the third and fourth bits of the virtual address 1572 areidentified as significant by this mask. This mask also identifies thethird and fourth bits of the destination identification as significant.Therefore, any MCPE having the third and fourth bits of the virtualaddress matching the third and fourth bits of the destinationidentification is selected. In this example, when the mask (0011) isapplied to the virtual address and applied to a destinationidentification in which the third and fourth bits are both zero, thenMCPEs 1550, 1553, 1556, and 1557 are selected. MCPEs 1550, 1553, 1556,and 1557 define a region 1560 and execute a particular function withinthe networked array 1500.

When the transmitted data comprises configuration data, manipulation ofthe selected MCPEs may comprise programming the selected MCPEs with anumber of configuration memory contexts. This programming may beaccomplished simultaneously with the execution of a present function bythe MCPE to be programmed. As the address masking selection schemeresults in the selection of different MCPEs or groups of MCPEs indifferent regions of a chip, then a first group of MCPEs located in aparticular region of the chip may be selectively programmed with a firstconfiguration while other groups of MCPEs located in different regionsof the same chip may be selectively programmed with configurations thatare different from the first configuration and different from eachother. The groups of MCPEs of the different regions may functionindependently of each other in one embodiment, and different regions mayoverlap in that multiple regions may use the same MCPEs. The groups ofMCPEs have arbitrary shapes as defined by the physical location of theparticular MCPEs required to carry out a function.

When the transmitted data comprises control data, manipulation of theselected MCPEs comprises selecting MCPE configuration memory contexts tocontrol the functioning of the MCPEs. As the address masking selectionscheme results in the selection of different MCPEs or groups of MCPEs indifferent regions of a chip, then a first group of MCPEs located in aparticular area of the chip may have a first configuration memorycontext selected while other groups of MCPEs located in different areasof the same chip may have configuration memory contexts selected thatare different from the first configuration memory context and differentfrom each other.

When the transmitted data comprises configuration and control data,manipulation of the selected MCPEs may comprise programming the selectedMCPEs of one region of the networked array with one group ofconfiguration memory contexts. Moreover, the manipulation of theselected MCPEs also comprises selecting a different group ofconfiguration memory contexts to control the functioning of other groupsof MCPEs located in different areas of the same chip. The regionsdefined by the different groups of MCPEs may overlap in one embodiment.

FIGS. 20-23 illustrate the use of the address masking selection schemein the selection and reconfiguration of different MCPEs or groups ofMCPEs in different regions of a chip to perform different functions inone embodiment. An embodiment of the present invention can be configuredin one of these illustrated configurations, but is not so limited tothese configurations. A different configuration may be selected for eachMCPE on each different clock cycle.

FIG. 20 illustrates an 8-bit processor configuration of a reconfigurableprocessing device which has been constructed and programmed according toone embodiment. The two dimensional array of MCPEs 1900 are located in aprogrammable interconnect 1901. Five of the MCPEs 1911-1915 and theportion of the reconfigurable interconnect connecting the MCPEs havebeen configured to operate as an 8-bit microprocessor 1902. One of theMCPEs 1914 denoted ALU utilizes logic resources to perform the logicoperations of the 8-bit microprocessor 1902 and utilizes memoryresources as a data store and/or extended register file. Another MCPE1912 operates as a function store that controls the successive logicoperations performed by the logic resources of the ALU. Two additionalMCPEs 1913 and 1915 operate as further instruction stores that controlthe addressing of the memory resources of the ALU. A final MCPE 1911operates as a program counter for the various instruction MCPEs 1912,1913, and 1915.

FIG. 21 illustrates a single instruction multiple data systemconfiguration of a reconfigurable processing device of one embodiment.The functions of the program counter 1602 and instruction stores 1604,1608 and 1610 have been assigned to different MCPEs, but the ALUfunction has been replicated into 12 MCPEs. Each of the ALUs isconnected via the reconfigurable interconnect 1601 to operate onglobally broadcast instructions from the instruction stores 1604, 1608,and 1610. These same operations are performed by each of these ALUs orcommon instructions may be broadcast on a row-by-row basis.

FIG. 22 illustrates a 32-bit processor configuration of a reconfigurableprocessing device which has been constructed and programmed according toone embodiment. This configuration allows for wider data paths in aprocessing device. This 32-bit microprocessor configured device hasinstruction stores 1702, 1704, and 1706 and a program counter 1708. FourMCPEs 1710-1716 have been assigned an ALU operation, and the ALUs arechained together to act as a single 32-bit wide microprocessor in whichthe interconnect 1701 supports carry in and carry out operations betweenthe ALUs.

FIG. 23 illustrates a multiple instruction multiple data systemconfiguration of a reconfigurable processing device of one embodiment.The 8-bit microprocessor configuration 1802 of FIG. 20 is replicatedinto an adjacent set of MCPEs 1804 to accommodate multiple independentprocessing units within the same device. Furthermore, wider data pathscould also be accommodated by chaining the ALUs 1806 and 1808 of eachprocessor 1802 and 1804, respectively, together.

Thus, a method and an apparatus for retiming in a network of multiplecontext processing elements have been provided. Although the presentinvention has been described with reference to specific exemplaryembodiments, it will be evident that various modifications and changesmay be made to these embodiments without departing from the broaderspirit and scope of the invention as set forth in the claims.Accordingly, the specification and drawings are to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. A method for locally controlling a first multiplecontext processing element (MCPE) of a plurality of MCPEs, the firstMCPE having network ports connecting the plurality of MCPEs to the firstMCPE, the first MCPE being configured to store one or more contexts, themethod comprising: manipulating a context of the first MCPE in responseto control information and configuration information, wherein theplurality of contexts include a plurality of major contexts ofconfiguration memory describing the operation of the first MCPE andwherein at least one of the plurality of major contexts of configurationmemory includes at least one minor context.
 2. The method of claim 1,wherein manipulating the context further comprises selecting a contextto control the function of the first MCPE.
 3. The method of claim 1,wherein manipulating the context further comprises programming the firstMCPE with a configuration memory context.
 4. The method of claim 3,wherein programming the first MCPE is performed simultaneously with theexecution of a present function by the first MCPE.
 5. The method ofclaim 1, wherein the first MCPE receives the control information from atleast one MCPE and wherein the control information comprises stateinformation.
 6. The method of claim 1, wherein the first MCPE receivesthe control information from a memory of at least one MCPE.
 7. Themethod of claim 1, wherein the the control information comprisesmaintained data.
 8. The method of claim 7, wherein the maintained datacomprises a current configuration state of the first MCPE.
 9. The methodof claim 8, further comprising feeding the current configuration stateof the first MCPE back to the first MCPE through a feedback path. 10.The method of claim 1, wherein manipulating one of the plurality ofcontexts is performed locally at the first MCPE.
 11. The method of claim1, wherein the first MCPE receives the control information from at leastone MCPE.
 12. The method of claim 1, wherein the first MCPE receives thecontrol information from a MCPE adjacent to the first MCPE.
 13. Themethod of claim 1, wherein the first MCPE receives the controlinformation from an external memory.
 14. The method of claim 1, whereinthe first MCPE receives at least one bit over a multiple level networkfrom at least one MCPE, the at least one bit representative of at leastone configuration context of the at least one MCPE.
 15. The method ofclaim 1, further comprising the first MCPE providing the controlinformation to at least one MCPE of the plurality of MCPEs, the controlinformation for manipulating the context.
 16. The method of claim 1,wherein the configuration information comprises data of a currentconfiguration of the first MCPE.
 17. The method of claim 1, wherein theconfiguration information comprises data of a previous configuration ofthe first MCPE.
 18. The method of claim 1, wherein the configurationinformation comprises state information of the first MCPE.
 19. Themethod of claim 1, wherein the configuration information comprises asignal received commonly by a plurality of MCPEs.
 20. The method ofclaim 1, wherein one or more major contexts contain data describinglocal network switching.
 21. The method of claim 1, wherein each majorcontext of configuration memory includes a plurality of minor contexts.22. The method of claim 21, wherein the plurality of minor contextscomprise contexts of configurations of network ports of the first MCPE.23. The method of claim 21, wherein one of the minor contexts isindependently writable.
 24. The method of claim 21, wherein one of theminor contexts comprises a clear mode.
 25. The method of claim 21,wherein one of the minor contexts comprises a freeze mode.
 26. Themethod of claim 21, wherein one of the minor contexts comprises auser-defined operation.
 27. The method of claim 1, wherein one of themajor contexts is programmable.
 28. The method of claim 27, wherein theprogrammable major context is for user-defined operations.
 29. Themethod of claim 1, wherein one of the major contexts is hardwired. 30.The method of claim 29, wherein the hardwired major context comprises areset state.
 31. The method of claim 29, wherein the hardwired majorcontext comprises a local stall mode.
 32. The method of claim 1, furthercomprising: assigning a virtual identification (VID) to the first MCPE;transmitting data comprising an address mask to the first MCPE;comparing the VID masked with the address mask to a masked destinationidentification; and selecting one of the plurality of contexts inresponse to the transmitted data when the masked VID matches the maskeddestination identification.
 33. The method of claim 1, furthercomprising programming the first MCPE with data of the plurality ofcontexts during the execution of a present function by the first MCPE.34. The method of claim 1, wherein manipulating one of the plurality ofcontexts is performed during execution of a second context in the firstMCPE.
 35. In a first multiple context processing element (MCPE) in anetwork of a plurality of MCPEs, the first MCPE having network portsthat connect the plurality of MCPEs to the first MCPE, comprising: amemory configured to store a plurality of contexts, wherein theplurality of contexts include a plurality of major contexts ofconfiguration memory describing the operation of the first MCPE andwherein at least one of the plurality of major contexts of configurationmemory includes at least one minor context; and a controller coupled tothe memory wherein the controller is configured to manipulate one of theplurality of contexts in response to control information andconfiguration information.
 36. The MCPE of claim 35, wherein thecontroller manipulates one of the contexts by selecting a context tocontrol the function of the first MCPE.
 37. The MCPE of claim 35,wherein the controller manipulates one of the contexts by programmingthe first MCPE with a configuration memory context.
 38. The MCPE ofclaim 37, wherein the controller programs the first MCPE simultaneouslywith the first MCPE executing a present function.
 39. The MCPE of claim35, wherein the control information comprises state information from atleast one MCPE.
 40. The MCPE of claim 35, wherein the controlinformation comprises information from a memory of at least one MCPE.41. The MCPE of claim 35, wherein the control information comprisesmaintained data.
 42. The MCPE of claim 41, wherein the maintained datacomprises a current configuration state of the first MCPE.
 43. The MCPEof claim 42, further comprising a feedback path to the first MCPE,wherein the current configuration state is provided to the first MCPEthrough the feedback path.
 44. The MCPE of claim 35, wherein thecontroller manipulates one of the plurality of contexts locally at thefirst MCPE.
 45. The MCPE of claim 35, wherein the first MCPE receivesthe control information from at least one MCPE.
 46. The MCPE of claim35, wherein the first MCPE receives the control information from a MCPEadjacent to the first MCPE.
 47. The MCPE of claim 35, wherein the firstMCPE receives the control information from an external memory.
 48. TheMCPE of claim 35, wherein the first MCPE receives at least one bitreceived over a multiple level network from at least one MCPE, the atleast one bit representative of at least one configuration context ofthe at least one MCPE.
 49. The MCPE of claim 35, wherein the first MCPEprovides the control information to at least one MCPE of the pluralityof MCPEs, and wherein the controller utilizes the control information tomanipulate the context.
 50. The MCPE of claim 35, wherein theconfiguration information comprises data of a current configuration ofthe first MCPE.
 51. The MCPE of claim 35, wherein the configurationinformation comprises data of a previous configuration of the firstMCPE.
 52. The MCPE of claim 35, wherein the configuration informationcomprises state information of the first MCPE.
 53. The MCPE of claim 35,wherein the configuration information comprises a signal receivedcommonly by at least some of the plurality of MCPEs.
 54. The MCPE ofclaim 35, wherein one or more major contexts contain data describinglocal network switching.
 55. The MCPE of claim 35, wherein each majorcontext of configuration memory includes a plurality of minor contexts.56. The MCPE of claim 55, wherein the plurality of minor contextscomprise contexts of configurations of network ports of the first MCPE.57. The MCPE of claim 55, wherein one of the minor contexts isindependently writable.
 58. The MCPE of claim 55, wherein one of theminor contexts comprises a clear mode.
 59. The MCPE of claim 55, whereinone of the minor contexts comprises a freeze mode.
 60. The MCPE of claim55, wherein one of the minor contexts comprises a user-definedoperation.
 61. The MCPE of claim 35, wherein one of the major contextsis programmable.
 62. The MCPE of claim 61, wherein the programmablemajor context is for user-defined operations.
 63. The MCPE of claim 35,wherein one of the major contexts is hardwired.
 64. The MCPE of claim63, wherein the hardwired major context comprises a reset state.
 65. TheMCPE of claim 63, wherein the hardwired major context comprises a localstall mode.
 66. The MCPE of claim 35, wherein a virtual identification(VID) is assigned to the first MCPE; data comprising an address mask istransmitted to the first MCPE the VID masked with the address mask iscompared to a masked destination identification; and the controllerselects one of the plurality of contexts in response to the transmitteddata when the masked VID matches the masked destination identification.